Are they moved to filters?
Yes, you need to generate a filter that includes the question.body, question.comments, and question.answers fields. There are shorthand filters (i.e. _bca) that will do this for upgrade compatibility, but their use is discouraged and you're better off just making a filter that contains exactly what you want anyway.
You have 2 questions:
"How do I exclude records based on the presence of a certain field?"
Answer: The API will not do this for you; your code must filter out these results.
"(How do I ) return only open questions?"
Answer: Use the /search/advanced route.
Exclude records where field is present:
The API does not do this for any field, and seems unlikely ...
The inname parameter restricts the results of a name search to only those that contain the specified substring. The following methods support it:
filtering on badge, user, or tag names, as applicable.